The present invention is directed to a catheter having an enhanced ablation electrode with having a hydrogel layer.
Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity.
In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the chamber of the heart which is of concern. Within the heart, the ability to control the exact position and orientation of the catheter tip is critical and largely determines how useful the catheter is.
A typical ablation procedure involves the insertion of a catheter having a tip electrode at its distal end into a heart chamber. A reference electrode is provided, generally taped to the skin of the patient. RF (radio frequency) current is applied to the tip electrode, and current flows through the media that surrounds it, i.e., blood and tissue, toward the reference electrode. The distribution of current depends on the amount of electrode surface in contact with the tissue as compared to blood, which has a higher conductivity than the tissue. Heating of the tissue occurs due to its electrical resistance. The tissue is heated sufficiently to cause cellular destruction in the cardiac tissue resulting in formation of a lesion within the cardiac tissue which is electrically non-conductive. During this process, heating of the electrode also occurs as a result of conduction from the heated tissue to the electrode itself. If the electrode temperature becomes sufficiently high, possibly above 60xc2x0 C., a thin transparent coating of dehydrated blood protein can form on the surface of the electrode. If the temperature continues to rise, this dehydrated layer can become progressively thicker resulting in blood coagulation on the electrode surface. Additionally, the irritation of the endocardial tissue, as well as the patient""s natural foreign body reaction to the presence of the electrode, results in the initiation of the inflammatory response and subsequent fibrous capsule development. The fibrous capsule increases in thickness in an attempt by the body to wall-off the foreign material.
Thus, a need exists for an improved catheter design that minimizes irritation and counters, delays or suppresses the occurrence of the inflammatory response and therefore the growth of the fibrous capsule.
The present invention is directed to a catheter having an improved electrode that minimizes irritation to the heart tissue and counters the occurrence of foreign body reactions. In one embodiment, the invention is directed to a catheter comprising an elongated, flexible catheter body having proximal and distal ends and at least one lumen extending therethrough. At least one electrode, such as a tip electrode or ring electrode, is mounted on the distal end of the catheter body, wherein the electrode comprises a base material having an outer surface and a hydrogel layer applied over at least a portion of the outer surface of the base material. Preferably a drug or other therapeutic agent is incorporated into the hydrogel layer.
In another embodiment, the invention is directed to an ablation system comprising a catheter as described above and a source of radio frequency energy electrically connected to the electrode.
In another embodiment, the invention is directed to a method for ablating tissue in a patient. The method comprises introducing the distal end of a catheter as described above into the patient so that the electrode is in contact with the tissue to be ablated and applying energy to electrode, thereby creating a lesion in the tissue.